Vapor phase nitration of aliphatic hydrocarbons in the presence of ozone



. oxygen-ozone mixture.

' "The improved process "yields and conversions of both nitro hydrocarbons and oxidation products such as alcohols, aldehydes, acids, .etc.,

consists essentially'of conducting'the vapor phase nitra- 'tion of aliphatic hydrocarbons at temperatures ranging from 200 to 500- C. with a nitrating agent suchas DRGCARBGNS IN THE PRESENCE F ()ZONE Norman W. Standish and Gustave B. Bachman, Lafayette,

11:141., assignors to Purdue Research Foundation, Lafayette, Ind, a corporation of Indiana No Drawing. Filed Nov. 13, 1959, Ser. No. 852,625

. 9 Claims. (Cl. 260-644) Our invention relates to the, nitration of aliphatic hydrocarbons. More particularly, it pertains to the produc- 1 tion of nitro hydrocarbons by the vapor phase nitration vapor phase nitration of paraffins such as ethane, pro- .pane, butane and the like, by means of nitric acid or nitrogen dioxide, that of Landon, described in US. Patent No. 2,161,475, pertaining to the nitration of methane by means of nitric acid, and that of Bachman et a1. U.S. Patent No. 2,597,698, pertaining to the use of regulated amounts of halogen, halogen-containing compounds, or

halogen-oxygen mixtures in the vapor phase nitration of aliphatic hydrocarbons by means of nitric acid or oxides y of nitrogen.

1 All of the prior art processes are open to a number of serious objections, the most important of which have been the low yields based on hydrocarbons used, low conversions based on the nitric acid used, onthe corrosive I nature of thereactants and products of reactions. We

have now discovered that the conversions and yields of nitr o'hydrocarbons, and/or the yields of valuable oxidation lay-products when hydrocarbons are nitrated in the vapor phase, can be improved by effecting the nitration in the presence of regulated amounts of an oxygen-ozone mixture. A further advantage of our invention lies in the fact that we are able to alter and, in some measure, control the distribution of nitration products by use of oxygen-ozone mixtures.

The use of oxygen in the manufacture of nitroalkanes by the vapor phase nitration of paraflin hydrocarbons is known, being described and claimed in US. Patent No. 7 2,609,401 by Hass and Alexander. It has not been previously known, however, that advantageous eifects such mlindicated above could be obtained by the use of an whereby we obtain increased nitric acid or oxides of nitrogen and adding an oxygenozone mixture to the reaction. For each mole of nitric l acid or oxide nitrogen used, we have found that from f 7to about 35' moles of hydrocarbons, from about 0.01 to 0.10 or 1.0 mole of ozone and not more than about 2.0 moles of molecularoxygen should be used. By carrying out the nitration'with such amounts of materials, the

conversions to nitro hydrocarbons are increased under some conditions by as much as 50% over those obtained the method 'of nitration in the presence of oxygen and by more than 100% ov'er those obtainedby the conventional methods of nitration in'the absence of oxygen. When control? of the distribution of nitrohydrocarbon United States Patent 0 VAPOR PHASE NITRATEQN 0F ALIPHATIC HY Q a Our process is, in general, applicable tothenitrati'on. of aliphatic hydrocarbons which are gaseous under the conditions of the process, i.e. at temperatures between 200 and 500 C. Our process is especially. advantageous for the nitration of paraflins, such as etha'rretpropane,

n-butane, isobutane, the pentanes, the hexanes, the heptanes, and the octanes; but it is also applicable to other aliphatic hydrocarbons, such as, for instance, the cycloparafiins. 7

Our process may be satisfactorily carried out over a wide temperature range, i.e. 200 to 500 C., depending upon the hydrocarbon being nitrated, the product desired and other conditions. However, the reaction time must be altered in accordance with the temperature used; substantially longer times being required for the lower temperatures and substantially shorter times being required for the higher temperatures for optimum conversion of nitric acid to nitro hydrocarbons. The particular hydrocarbon being nitrated also has some effect on temperature and contact time. For parafiins, nitration temperatures decrease somewhat for a given contact; time as chain length and branching increase. In general, the contact times used when an oxygen-ozone mixture is present do not differ substantially from those used in nitrations carried out according to the conventional methods, with or without molecular oxygen present except that with a given contact time, a slightly lower temperature can be employed. Accordingly, incarrying out our improved process the temperatures, reaction times, and space velocities are regulated in the same general manner as in the prior art processes. v. y

The surface to volume ratioof the reactor in which the nitration is carried out has an effect on the results. "In general, increased yields and conversions of nitroparaflins are obtained when ozone-oxygen mixtures are employed in reactors having a surface to volume ratio in the range of about 1 to 3. On the other hand, the use of ozoneoxygen mixtures in reactors having higher surfiace to volume ratios than about 3 results in varieddistribution of nitroparatrins and higher yields of valuable oxidation by-products. The eifect of surface to volume ratio is not sharply defined and the other operating conditions can be adjusted to get the best possible results with a particu lar reactor.

While the exact amount of ozone to be added varies somewhat with the temperature, the hydrocarbon to nitric acid ratio, the amount of oxygen, the contact time, and. the type of reactor employed, it can be said in general that greatly improved results BIB obtained when catalytic proportions of from about 0.01 to 0.10 rnole'of ozone is added per mole of nitric acid. Larger quantities than 0.10 mole of ozone produce diminishing yields of nitroparaffins and increased yields of oxidation products .probably due, at least in part, to the increased proportion of oxygen in the oxygen-ozone mixture. Such larger quantities also have an efiect on the distribution of nitropar-affin products as do quantities within the range mentioned above. Smaller quantities than 0.01 mole of ozone/mole nitric acid can also be used, but diminished etlects on the yield of nitroparaffins may .be encountered.

The method of employing the' oxygen -ozone mixture in our improved process can be varied somewhat without decarbon before or after the introduction of'the nitric acid.

We have generally found it advantageous, however, to introduce the oxygen-ozone mixture into the hydrocarbon stream prior to mixing with the nitric acid vapors.

products is desired, higher amounts of ozone than men- 7 The molecular oxygen used in our process to generate ozone can be substantially pure oxygen, or oxygen mixed source, the catalytic etfect of the ozone appears to be reduced since the amount of actual oxygen in the air is reduced. This is not to be construed as meaning that air cannot be used as the oxygen source since some catalytic action is observed; that is, the yields and conversions are greater under some conditions than when no ozone is present. When air is used we prefer to use a mixture with oxygen as well as the ozone. This same effect of air on normal catalytic elfects has been noted previously in US. Patent 2,597,698.

As' we have pointed out, the distribution of nitrohydrocarbons produced in our newprocess is altered from that obtained in normal nitration in the absence of ozone or ozone and oxygen. By earring out the nitration with added ozone, the formation of higher molecular weight nitro' hydrocarbons is favored. While from the point of view of yields of nitrohydrocarbons the use of in excess of 0.10 mole of ozone is generally not desirable, the use of both' lower andhigher amounts of ozone is effective in altering the distribution of the nitrohydrocarbon formed during the nitration, the distribution being determined by the-amount of ozone used.

The following specific examples will illustrate the operation of our process. It is distinctly understood, however, that we are not limited to either the specific operating conditions and the specific amounts of reactants shown therein.

EXAMPLE I A reaction mixture consisting of 5.38 moles of propane and 0.54 mole of 69% nitric acid was passed in the vapor phase through an electrically heated Pyrex glass reactor which had a. total reaction volume of about 650 ml. The reaction. temperature was 425 C.,-.the contact time was 2.59 seconds, and the surface to volume ratio 3.14 cm.- (run No; H48).

In a similar run a reaction mixture consisting of 4.68 moles of propane, 0.47 mole of 60% nitric acid, and 0.75 mole of oxygen was passed through the identical apparatus at 425 C., and a contact time of 2.26 seconds (run No. H-ll).

Using the identical apparatus, a similar run was made with a reaction mixture consisting of 4.68 moles of propane, 0.47 mole of 69% nitric acid, 0.56 mole of oxygen, and 0.0196 mole-f ozone at 425 C., and a contact time of 2.3 2 seconds (run No. H-14).

The results of these three runs, given in Table I below, show that the addition of ozone to the nitration reaction gives increased yields based. on propane and conversions based on nitric acid over those obtained in normal nitration, or nitration with oxygen added to the reaction mixture.

EXAMPLE II In order to determine the effect of varying the amounts of the oxygen-ozone mixture in the nitration of propane, additional runs were made in the same reactor described in Example I. In these runs the rat-i0 of propane to nitric acid wasmaintained constant. Table 11 indicates that the addition of an oxygen-ozone mixture results in 5 increased conversions and yields when the mole ratio of oxygen to nitric acid is maintained below about 2.0. The optimum conditions for increased conversions and yields in this particular reactor appear to be at an oxygen to nitric acid ratio of 1.20 and an ozone to nitric acid ratio of 0.042. However, it can be seen that at higher oxygen and ozone to nitric acid ratios, an increase in oxidation products is obtained.

Table II THE EFFECT OF VARYING THE OXYGEN-OZONE MIX- TUBE FEED IN THE VAPOR PHASE NITRATION OF PROPANE Run No Hl3 11-14 Iii-15 H-lfi Temperature, C 415 425 425 425 Contact time. sec 2. 42 2. 32 2. 22 2. 16 Reaetants, Mole ratio:

CsHg/HNO; 10 10 10 10 O2/1-INO3 p 0.70 1.20 1.59 2.06 Os/HNOs 0. 024 0. 042 0. 061 0.076 Percent C011versionHNOs to RN 0:. 41. 7 56. 4 4l. 5 29. 2 Yields on Propane (percent):

RNO 28.9 32.5 24.1 154 C01... 2.8 2.5 2.8 3.9 CO 7.0 14.3 16.2 19.5 Ethylene 12.4 10. 7 7. 4 12. 4 Propylene 25.3 20. 1 29. 1 23. 3 Carbonyl Compounds 23. 7 19. 9 20. 5 25. 5

EXAMPLE III A reaction mixture consisting of 5.38 moles of propane and 0.54 mole of 69% nitric acid was passed through the reactor described in Example I at 425 C. and contact time of 2.59 seconds (run H-8).

In a similar run a reaction mixture consisting of 4. 68 moles of propane, 0.47 mole of 69% nitric acid, and 0.13 mole of oxygen (as air) was passed through the identical apparatus at 425 C., and a contact time of 2.33 seconds (run H-l9) Using the identical apparatus, a similar run was made with a reaction mixture consisting of 4.68 moles of propane, 0.47 mole. of 69% nitric acid, 0.156 mole of oxygen (as air) and 0.039 mole of ozone at 425, and a contact time of 2.25 seconds (run I-I-23).

The results of these three runs, given in Table III, show that the presence of an air-ozone mixture in the nitration reaction increases the yields based on propane and conversions based on nitric acid over those obtained using the optimum conditions for normal nitration, or nitration With air added to the reaction rnixture.

Table III EFFECT OF OZONE ON THE NITRA'IION REACTION Run No H-8 II-19 H-23 Temperature, C 425 425 425 Contact time, sec 2. 59 2. 25 2. 25 Reaetants, Mole ratio:

C3H /ITNO3 1O 10 10 none 0. 372 0. 372 none none 0. 039 Percent Conversion-HNOa to RNOz 24.8 23.3 30.8 Yields on Propane (percent):

Oz 25.0 25. 6 28.1 002" 2. 5 8.1 4.1 00 9.6 11. 4 9.9 Ethylen 19.3 10.5 9.0 Propylene" 28.8 30.8 37.4 Carbonyl C 14. 8 19. 2 16. 7

EXAMPLE IV Additional runs were made todetermine the elfect of varying the amounts of the oxygen (as air)-ozone mixture in the vapor phase nitration of propane. These runs were made in the same reactor described in Example I maintaining a constant ratio of propane and nitric acid. The results are shown inTable IV. The optimum oxygen (as air) to nitric acid ratio and ozone to nitric acid ratio under the conditions employed and in this particular reactor appear to be 0.372 and 0.039 respectively.

5 Table IV THE EFFECT OF VARYING THE AIR-OZONE FEED IN THE VAPOR PHASE NITRATION OF PROPANE Run No 11-21 H-22 11-23 11-24 Temperature, C 425 425 425 425 Contact Time, see 2. 41 2. 33 2. 25 2.18 Reaetants, Mole Ratloz Cam/ENG; 10 10 10 10 Or (as air)/HNOa 0. 190 0.282 0.372 0. 462 Os/HNO: 0.015 0. 027 0. 039 O. 035 Percent Conversion-ENOa to RN 22. 3 24. 5 30. 8 28. 0 Yields on Propane (Percent):

RNOz 27. 9 23. 8 28. 1 25. 7 7.0 4. 4 4.1 4. 2 10.0 9. 2 9. 9 11.3 9.0 10.5 9. 0 14.1 30.1 36. 9 37. 4 26. 7 Carbonyl compounds 16.4 15. 3 16.7 18.0

EXAMPLE V Additional runs were made to show the efiect of ozone on the distribution of the nitroparaifin products in the vapor phase nitration of propane. In these runs, the nitration equipment described in Example I was used and the same procedure employed. The results are shown in Table V.

Table V EFFECT OF OZONE ON THE PRODUCT DISTRIBUTION IN THE VAPOR PHASE NITRATION OF PROPANE EXAMPLE VI Using a Pyrex glass reactor having a volume of 6 65 m1. and a surface to volume ratio of 1.1 cm.- a series of runs was made at a propane to nitric acid ratio of 10 to 1 without oxygen or ozone, with oxygen, and with oxygen and ozone, the amount of oxygen above being in a molar ratio of 1 to 1 mole of nitric acid and the amount of ozone being .04 mole per mole of nitric acid over a range of temperatures from 332 C. to 440 C. The optimum conversion was obtained at 413 C. when no oxygen or ozone was used, 374 C. when oxygen only was employed and 352 C. when oxygen and ozone were used.

The percent distribution of nitroparaflin products obtained in the three runs is shown in the following table:

Now having disclosed our invention, what we claim is:

1. In the vapor phase nitration of aliphatic hydrocarbons at temperatures ranging from 200 to 500 C. with a nitrating agent selected from the group consisting of nitric acid and nitrogen dioxide, the step which comprises adding catalytic proportions of ozone with the reactants in the said nitration.

2. The process of claim 1 wherein a mixture of ozone and oxygen is added with the reactants.

3. The process of claim 1 wherein in excess of 0.01 to 1.0 rnole of ozone per mole of nitrating agent is added with the reactants.

4. The process of claim 1 wherein 0.01 to 0.10 mole of ozone per mole of nitrating agent is added with the reactants.

5. The process of claim 1 wherein 0.01 to 1.0 mole of ozone and not in excess of 20 moles of molecular oxygen per mole of nitrating agent are added with the reactants.

6. The process of claim 1 wherein the reaction is effected with 7 to 35 moles of saturated aliphatic hydrocarbons per mole of nitrating agent and 0.01 to 1.0 mole ozone and not in excess of 2.0 moles of molecular oxygen per mole of nitrating agent are added with the reactants.

7. In the vapor phase nitration of aliphatic hydrocarbons at temperatures ranging from 200 to 500 C. with a nitrating agent selected from the group consisting of nitric acid and nitrogen dioxide, the step comprising adding from about 0.01 to 1.0 mole of ozone per mole of nitrating agent to the reactants in said nitration.

8. In the vapor phase nitration of an aliphatic hydrocarbon at temperatures from about 200 to 500 C. with a nitrating agent selected from the group consisting of nitric acid and nitrogen dioxide, the step comprising adding from about 0.01 to 0. 1 mole of ozone and not in excess of 2:0 moles of molecular oxygen per mole of nitrating agent with the reactants in the said nitration.

9. The process of claim 8 wherein the aliphatic hydrocarbon is propane.

References Cited in the file of this patent UNITED STATES PATENTS 1,325,168 Perruche Dec. 16, 1919 1,348,874 Guye Aug. 1 0, 1920 2,512,587 Stengel June 20, 19-50 

1. IN THE VAPOR PHASE NITRATION OF ALIPHATIC HYDROCARBONS AT TEMPERATURES RANGING FROM 200 TO 500*C. WITH A NITRATING AGENT SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID AND NITROGEN DIOXIDE, THE STEP WHICH COMPRISES ADDING CATALYTIC PROPORTIONS OF OZONE WITH THE REACTANTS IN THE SAID NITRATION. 